Our transcription: One of the benchmark discoveries in geology over the last half-century is the origin of mountain ranges. Continents and oceanic crust have collided or subducted at tectonic plate margins. Mountain ranges have been formed, and processes of erosion have torn them down. Eventually, the continents are split apart by renewed plate divergence and are on their way to new collisions, often forming a supercontinent. This tectonic cycle, sometimes referred to as the "dance of the continents" has been repeated many times in the geologic past with each complete cycle lasting several hundred million years. Some aspects of this tectonic dance have surprisingly complicated steps. Alaska, for example, is largely composed of plate fragments that have been packed together by successive collisions. Some of these terranes have been tectonically transported thousands of kilometers by sea floor spreading and strike slip faulting before colliding with North America to form Alaska.The Mediterranean Sea is a shrinking ocean basin caught in a collision between the colliding continents of Africa and Europe, the famous volcanoes and earthquakes and intensely deformed mountains of this region are evidence of the profound mountain building that accompanies the death of an ocean. Tectonic cycles and mountain building are nearly as old as the Earth itself, and the forecast for the geologic future is continued change, change in the ocean basins, and continents, and mountain ranges, that together are the face of the Earth. A map of the world a billion years from now will bare a scant resemblance of the world we know today.